In the formulation of foaming aerosol products, an essential component is the propellant which is used to dispense the liquid concentrate. In manufacturing, the liquid concentrate is first filled into the aerosol can which is sealed with a valve cup and then the propellant is introduced via pressure filling. It is also possible to do under the cup filling where the propellant is filled and the valve cup sealed in one step. Commonly used propellants in the formulation of personal care products can be classified into two major groups: Compressed gases and Liquefied propellants.
Compressed Gases
Examples of compressed gases are nitrogen, carbondioxide, etc., which remain as gases in the aerosol can. Depending on the type of concentrate used, they can be partially solubilized in the liquid concentrate. The pressure that results from such a product can be controlled by the amount of propellant that is solubilized in the liquid concentrate and what is left in the head space. Compressed gases are not widely used in personal care products since the pressure drops over the life of the can when it is being used resulting in different spray characteristics, lower spray rates and poorer foam quality. However the advantage of compressed gases is that they are inexpensive compared to liquefied propellants.
Liquefied Propellants
They are so called because they are gases under normal temperature and pressure but become liquids under higher atmospheric pressure. The advantage of using liquefied propellants is that they maintain a constant pressure throughout the life of the can by converting from a liquid state to a gaseous state as the can is depleted. This provides the user with a product that does not vary too much in its properties. Commonly used liquefied propellants are hydrocarbons, hydrofluorocarbons and dimethylether. Fluorocarbons were the most widely used propellants up until the mid 1970's when their use was restricted because they were alleged to damage the ozone layer. Hydrocarbons are now the propellant of choice because they are readily available and are less expensive than hydrofluorocarbons. Hydrocarbons used in the personal care industry are usually mixtures of Isobutane, n-butane and propane. These three are blended to give the desired pressure. For example, hydrocarbon A-46 is a mixture of 15.1% by weight of propane and 84.9% by weight of isobutane blended to give 46 psig pressure at 70 F. If lower pressures are desired, then the propellants are used as is. For example, n-butane has a pressure of 17 psig at 70 F. and Isobutane has a pressure of 31 psig at 70 F. which can be used without blending.
Hydrofluorocarbons belong in the liquefied propellant group but are not widely used because of their expense. The most commonly used hydrofluorocarbon is Dymel 152A manufactured by Dupont. Dymel 152A has a pressure of 62 psig at 70 F. which makes it desirable for a number of applications. In hair sprays for example, this pressure is lowered by its solubility in the alcohol base which gives an even soft spray and in hair mousses, it is used to give a rich dense foam. Dymel 152A is also denser than hydrocarbons which is an advantage when filling cans to a desired weight.
Dimethyl ether is another good propellant. Unlike hydrocarbons, it is extremely soluble in water. It is also reasonably priced and as a result has found its place in water based hair spray formulations. Its use in mousses as a sole propellant is limited due to high solubility.
Formulation Considerations
In the formulation of mousse products, the choice and amount of propellant used plays a major role in the quality of the foam produced. The two propellants that are currently used in the U.S. are Dymel 152A ( known as Dymel 152 and 152A, available from E. I. Dupont, Wilmington, Del.) and Hydrocarbon A-17(n-butane). Formulation parameters that make these two propellants attractive are: Pressure of the finished product, which should be such that the amount dispensed is in an acceptable range and the product can be packaged in a suitable can. The density of the formulation which determines how much weight percent of the active that can be dispensed each time. The quality of the foam is also a function of the type of propellant used--Dymel 152A gives a rich dense foam while hydrocarbon foams are more airy. The amount of propellant used in hair mousse formulations is typically between 4-9% by weight. At propellant levels higher than 9% by weight, the foam produced is dry whereas at lower levels below 4% the foam is not dense and runny.
Although other ingredients in the formulation also play a role in the quality of the foam especially the level and type of surfactant used, it could generally be stated that Dymel 152A as a propellant has advantages over hydrocarbon dispensed products in producing a rich foam, and a dense foam which carries with it a higher active level. On the other hand, its disadvantages are is its cost and the resultant product has a higher pressure requiring it to be packaged in a more expensive can to meet department of transportation regulations.
The problem that this invention has attempted to solve is how to get all of the advantages of the Dymel 152A propelled product to combine with all of the advantages of the hydrocarbon while keeping the cost of the finished product and the can to be at its lowest level.
In brief, the present invention is directed towards producing a mousse product composition that is dispensed with a particular ratio of Dymel/hydrocarbon propellant to maximize its foam quality while minimizing the cost of the product and the can it is packaged in.
Accordingly, it is an object of this invention to produce a foam that is rich in quality but yet at the same time is less expensive and can be packaged acceptably without using an expensive quality can.
The invention provides a propellant composition having low vapor pressure, good foaming properties.
A propellant composition that is lower in vapor pressure is safer to use and handle and can be dispensed from lighter, less expensive containers.
Another measure of propellant is the foam which it produces. A preferred foam will be creamy feeling and looking and will have a slippery feel. An added advantage is if the propellant can produce a shiny foam. These characteristics are all achieved by the present invention.